From: "Ara.T.Howard" <ahoward@...>
Date: 2004-03-09T23:44:40+09:00
Subject: Re: How do I enforce variable declarations in Ruby?

On 9 Mar 2004, Bill Atkins wrote:

> Is there any way to require that all variables and class attributes be
> predeclared?  I'm looking for something similar to Perl's strict
> pragma.  It would prevent bugs like this:
> 
> class Demo
>     def initialize
>         @count = 0
>     end
> 
>     def anotherfunc
>         @cout += 1
>     end
> 
>     def get_count
>         @count
>     end
> end
> 
> d = Demo.new
> puts d.get_count
> d.anotherfunc
> d.get_count
> 
> Note the typo in anotherfunc.  This code was intended to output a zero
> followed by a one, but because of the typo, will output two 0's.
> 
> Is there any way to prevent errors like this from happening?


method one - use ruby's ability to declare accessors

  ~ > cat a.rb
  class Demo
    attr :count, 1 
    def initialize
      self.count = 0
    end
    def anotherfunc
      self.cout += 1
    end
    def get_count
      self.count
    end
  end

  d = Demo.new
  puts d.get_count
  d.anotherfunc
  d.get_count

  ~ > ruby a.rb
  0
  a.rb:7:in `anotherfunc': undefined method `cout' for #<Demo:0x400a3cc8 @count=0> (NoMethodError)
          from a.rb:16


method two - turn on warnings

  ~ > cat b.rb
  $VERBOSE = true
  class Demo
    def initialize
      @count = 0
    end
    def anotherfunc
      @cout += 1
    end
    def get_count
      @count
    end
  end

  d = Demo.new
  puts d.get_count
  d.anotherfunc
  d.get_count

  ~ > ruby b.rb
  0
  b.rb:8: warning: instance variable @cout not initialized
  b.rb:8:in `anotherfunc': undefined method `+' for nil:NilClass (NoMethodError)
          from b.rb:17

> I find it hard to believe that a language as well-designed as Ruby would
> lack this simple feature.

it's the '-w' switch ($VERBOSE = true)

-a
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